Was it that they couldn’t hear the ringer because Lady Gaga was playing too loud?

A Lincoln Square co-op is suing a neighboring club for $11 million for refusing to answer a dedicated noise-complaints hot line — one a judge ordered them to install after numerous infractions.

The board of 61 W. 62nd St. hauled the Empire Hotel Rooftop Bar and Lounge to court Friday to force the club to pick up the phone — and turn down the volume.

“My clients feel that the hot line has been totally ineffective in part because they can’t even hear the phone ringing in the bar,” said the residents’ lawyer Steven Sladkus.

In 2010, a judge ordered the Empire to set up a phone line for the co-op to call when the bar’s thumping bass got too loud.

The luxury building had first sued the hotel in 2009 after “blaring club dance music, amplified deejay noise and pounding bass noise [got] so intense that it literally rattled the windows of many of the co-op’s apartments,” according to court papers.

The club purchased a cellphone reserved for calls from the neighbors to make noise complaints. It was supposed to be carried by the on-duty manager every night.

“Cooperative residents were encouraged to use this phone number so that defendants could quickly resolve any noise problems without court intervention,” the suit says.

The club also agreed to close its east terrace by 10 p.m. on weeknights and midnight on weekends.

The system worked for almost four years until Empire employees stopped picking up the calls in August, according to the Manhattan civil suit. The staff “rarely if ever answer the phone,” says the new claim.

Other times the irritated neighbors get an automated error message, the suit says.

Also “throughout August, September and into October 2014, [the bar] permitted large crowds to congregate on the east terrace,” past the agreed-upon closing times.

The suit says that “on Friday, Sept. 12, patrons in the smoking area of the east terrace made loud noises until at least 3:35 a.m.”